This invention relates to a solar cell and, more particularly, to a solar cell wherein the voltage is produced by paint layers that are applied by painting techniques.
A solar cell is a device which directly converts the energy of the sun into electrical energy by a photovoltaic process. The solar cell, also sometimes termed herein a photovoltaic cell, generates an electrical voltage and current based on the interaction of the incident solar energy with semiconductor materials in the solar cell. Solar cells are the primary energy source for many types of spacecraft such as communications satellites. Additionally, they are used in terrestrial locations such as remote sites that are not readily accessible to conventional electrical service.
The solar cell is based on a PN junction between layers of p-type semiconductor material and n-type semiconductor material. These semiconductor materials are typically a base semiconductor material doped to be p-type or n-type, as required. Various base semiconductor materials are used, with examples being silicon and gallium arsenide.
The solar cell is prepared by depositing or otherwise forming a layer of the n-type semiconductor overlying a layer of the p-type semiconductor. Appropriate electrical contacts to the layers are provided to collect the voltage and current that result when light is incident upon the layered structure, with one of the electrical contacts permitting the passage of light therethrough to the semiconductor layers.
Solar cells are expensive to fabricate and are fragile. The expense arises in part because solar cells are inherently relatively inefficient in converting solar energy to electricity, and it is therefore necessary to provide a large area of the solar cell to achieve large voltages and/or currents. The fabrication of layered semiconductor structures of a large size by conventional semiconductor deposition techniques is difficult and expensive, because the techniques are complex. The active components of the solar cell are mounted to a support such as a frame that orients the semiconductor materials toward the light source and also protects the components from physical damage. The semiconductor layers are fragile and easily broken during fabrication, assembly, transportation (such as spacecraft launch), and service (such as impact by micrometeorites).
Existing solar cells are highly useful but have practical shortcomings. There is a need for an improved solar cell that is less expensive to produce and more robust than available solar cells. The present invention fulfills this need, and further provides related advantages.
The present invention provides a solar (photovoltaic) cell and a method for its fabrication. The voltage-generating components of the solar cell are paints, which may be formulated and then applied using painting techniques rather than the complex semiconductor deposition techniques. The preparation of solar cells of arbitrarily large size is therefore straightforward and inexpensive, and the amount of frame-like support structure is minimal. The finished solar cells are mechanically robust and resistant to breakage, inasmuch as they are not brittle and a crack or fracture does not rapidly propagate through the solar cells as in the case of conventional solar cells. That is, the solar cells are robust against damage from vibration, impacts, and the like. The solar cells may be fabricated on a flexible support and stowed for transport, on a flat support, or on a curved support. These features are important advantages for solar cells to be used in space, for which launch costs on a weight or volume basis are high.
The solar cell itself may be tuned to the required wavelengths for optimal efficiency without resorting to multiple discrete layers of semiconductor material as in the case of conventional solar cell designs. A capacitive energy-storage paint layer may be added to store excess electrical charge for later use, reducing the battery storage requirements. The solar cell also aids in thermal control and dissipation of electrostatic charges that build up on the surface of the spacecraft over time.
While the primary focus of the present application is on the preferred use of the solar cell for spacecraft, it is also suitable for terrestrial power production. The solar cell may be applied to large areas of conventional structures. The paint solar cell may be applied, for example, to a roof or exterior wall both to protect structures and to generate electrical power.
In accordance with the invention, a solar cell comprises an active structure including a paint voltage source having a first paint layer structure comprising p-type pigment particles dispersed in a first-layer binder, and a second paint layer structure comprising n-type pigment particles dispersed in a second-layer binder, the second paint layer structure being in electrical contact with the first paint layer structure. The binders may be organic or inorganic. Filler particles may be present in either layer. The layers are preferably applied on top of each other in direct physical contact. The p-doped first paint layer structure may face the sun with the n-doped second paint layer structure thereunder, a xe2x80x9cp over nxe2x80x9d configuration. Alternatively, the n-doped second paint layer structure may face the sun with the p-doped first paint layer structure thereunder, an xe2x80x9cn over pxe2x80x9d configuration. Preferably, at least one of the layers, most preferably the layer facing the sun, is black in color to absorb the solar energy.
The solar cell further has an electrically conductive contact structure having a first electrically conductive contact to the first paint layer structure, and a second electrically conductive contact to the second paint layer structure. At least one of the first electrically conductive contact and the second electrically conductive contact permits light to pass therethrough to the paint voltage source.
The solar cell as described may be freestanding in some embodiments, or there may be a support to which the active structure is attached. The support may be of any operable type and physical configuration, such as flexible, rigid, flat, or curved.
In another embodiment, only one of the p-type layer and the n-type layer need be a paint, and the other may be a non-paint semiconductor.
Thus, a solar cell comprises an active structure including a voltage source having a p-type semiconductor layer structure and an n-type semiconductor layer structure in electrical contact with each other. At least one of the semiconductor layer structures is a paint layer structure comprising first-layer paint pigment particles dispersed in a first-layer binder. The first-layer paint pigment particles are selected from the group consisting of p-type pigment particles and n-type pigment particles. An electrically conductive contact structure has a first electrically conductive contact to a first one of the semiconductor layer structures, and a second electrically conductive contact to a second one of the semiconductor layer structures. At least one of the first electrically conductive contact and the second electrically conductive contact permits light to pass therethrough to the voltage source.
Spacecraft and other installations that generate electrical energy from solar cells experience periods of darkness during service. It is therefore necessary to store some of the generated electrical energy during periods of light in batteries or other energy storage devices for later use. The present approach provides a capacitive paint layer that may be used in conjunction with the paint solar cell. The capacitive paint layer stores electrical energy generated by the solar cell and may be later discharged through the load when the electrical energy is needed. The capacitive paint layer allows the heavy, expensive batteries to be reduced in number and size or eliminated completely from the electrical system.
The solar cell may therefore include a capacitor in electrical communication with, and typically painted upon, the electrically conductive contact that does not permit light to pass therethrough. The capacitive paint layer structure preferably comprises pyroelectric/ferroelectric pigment particles dispersed in a capacitive layer binder. A first side of the capacitive paint layer structure contacts the non-light-transmitting electrically conductive contact remote from the paint voltage source. A capacitor electrically conductive contact is in electrical communication with a second side of the capacitive paint layer structure remote from the first side, producing a capacitor between the electrically conductive contact of the paint voltage source and the capacitor electrically conductive contact.
A method for preparing a solar cell comprises the steps of preparing a liquid first paint comprising p-type pigment particles, a first-paint binder, and a first paint liquid vehicle, and preparing a liquid second paint comprising n-type pigment particles, a second-paint binder, and a second paint liquid vehicle. The solar cell is fabricated by applying a first layer of the liquid first paint and at least partially drying the liquid first paint by removing the first paint liquid vehicle, to leave a solid first paint layer structure comprising the p-type pigment particles and the first-paint binder, and applying a second layer of the liquid second paint and drying the liquid second paint by removing the second paint liquid vehicle, to leave a solid second paint layer structure comprising the n-type pigment particles and the second-paint binder. A first electrically conductive contact is formed to the solid first paint layer structure, and a second electrically conductive contact is formed to the solid second paint layer structure. At least one of the first electrically conductive contact and the second electrically conductive contact permits light to pass therethrough.
The present invention provides a major advance in the art of solar cells and photovoltaic generation of electrical power. Solar electrical power may be generated by a solar cell that is applied by painting. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.